Field of Invention
Various embodiments of the invention relate generally to an electronic device and, more particularly, to a semiconductor memory device and an operating method thereof.
Description of Related Art
Semiconductor memory devices may be classified into volatile and non-volatile memory devices.
Non-volatile memory devices operate at relatively lower write and read speeds than volatile memory devices, but they retain their stored data regardless of whether the supply power to the device is turned on or off, Therefore, a non-volatile memory device is employed for storing data which need to be maintained even in the absence of power supply to the device. Examples of non-volatile memory devices include read only memory (ROM), mask ROM (MROM) programmable ROM (PROM), erasable programmable ROM (EPROM), electrically erasable and programmable ROM (EEPROM), flash memory, phase-change random access memory (PRAM), magnetic RAM (MRAM), resistive RAM (RRAM) and ferroelectric RAM (FRAM). Flash memories are used widely and may be classified into NOR- or NAND-type memories.
Flash memories enjoy the advantages of both RAM and ROM devices. For example, flash memories may be freely programmed and erased similar to a RAM. Also, similar to a ROM, flash memories may retain their stored data even when they are not powered. Flash memories have been widely used as the storage media of portable electronic devices such as mobile phones, digital cameras, personal digital assistants (PDAs), and MP3 players.
Flash memory devices may be classified into two-dimensional (2D) semiconductor devices in which a string of memory cells is formed in a horizontal direction to semiconductor device substrate and three-dimensional (3D) semiconductor devices in which a string of memory cells is formed in a vertical direction to a semiconductor device substrate.